1. Field of the Invention
The present invention relates to electrochromic display devices using an electrochromic material such as WO.sub.3, MoO.sub.3, viologen etc. and, more particularly, to a construction and a driving method for such electrochromic display devices.
2. Description of the Prior Art
Japanese Published Unexamined Patent Application No. 53-17090 published Feb. 16, 1978 discloses the so-called charge transfer driving system characterized in that erasing voltage is applied to one or more colored display electrodes made of an electrochromic material, the amount of charge of the erasing voltage corresponding to a coloration depth of the colored display electrodes, and in that no current flows after completion of erasure so as to prevent further application of charge. By virtue of this function, however, any voltage is applied to a plurality of charges for coloration of all the display electrodes is intended to be kept constant as long as the applied voltage is less than a voltage which would cause an undesirable reaction such as resolution of the electrolyte, etc.
However, it has been difficult to accurately keep the total amount of charge for coloration constant, particularly, under an elevated temperature, so that the total amount reduced to thereby make coloration depth of the display electrodes faint, gradually.